There have been proposed techniques for improving effective permeability of a coil element. For example, Japanese Patent Application Publication No. 2016-072556 (hereinafter “the '556 Publication”) discloses a coil element including a core portion made of an isotropic magnetic material, a coil conductor wound around the core portion, an outer peripheral portion provided on a radially outer side of the coil conductor and made of an isotropic magnetic material, and anisotropic magnetic material layers provided on an upper surface and a lower surface of the coil conductor.
The coil element disclosed in the '556 Publication is configured such that the core portion and the outer peripheral portion are adjacent to the anisotropic magnetic material layer in a direction perpendicular to the coil axis of the coil conductor. Therefore, the magnetic flux generated from the coil conductor is incident on the core portion and the outer peripheral portion without largely changing its direction from the easy direction of magnetization to the hard direction of magnetization in the anisotropic magnetic material layer. Accordingly, in the coil element of the '556 Publication, the magnetic flux is not oriented in the hard direction of magnetization in the anisotropic magnetic material layer, resulting in a high effective permeability.
However, in the coil element disclosed in the '556 Publication, the magnetic flux deflects from the easy direction of magnetization of the anisotropic magnetic material layer in the region in which the magnetic flux runs from the core portion or the outer peripheral portion at a side of the coil conductor to above or below the coil conductor. The reason for this is as follows.
The magnetic flux generated in the coil element disclosed in the '556 Publication is oriented in a direction substantially parallel to the coil axis at a side of the coil conductor and is oriented in a direction substantially perpendicular to the coil axis above and below the coil conductor. Therefore, in the region in which the magnetic flux runs from the side of the coil conductor to above or below the coil conductor, the direction of the magnetic flux changes from the direction parallel to the coil axis to the direction perpendicular to the coil axis. In addition, in the coil element of the '556 Publication, when the magnetic flux runs from the side of the coil conductor where it is oriented in the direction parallel to the coil axis to above or below the coil conductor, the magnetic flux is incident on the anisotropic magnetic material layer provided above or below the coil conductor. The easy direction of magnetization of the anisotropic magnetic material layer is perpendicular to the coil axis, and therefore, in the region of the anisotropic magnetic material layer adjacent to the side of the coil conductor, the magnetic flux deflects from the easy direction of magnetization of the anisotropic magnetic material layer. This deflection is particularly significant in the vicinity of the coil conductor.
Thus, the effective permeability of the coil element of the '556 Publication is impaired due to the difference between the direction of the magnetic flux and the easy direction of magnetization in the region in which the magnetic flux runs from the side of the coil conductor to above or below the coil conductor.